A valve box is a device intended to be located at ground level so as to allow the access, using an appropriate key, to the operating member of a valve of a buried pipe, such as a water distribution pipe.
It is important for saving time and costs, but also for improved safety, to be able to detect the presence of such a pipe, and to localize it accurately, without digging the ground, nor destroying building, on the occasion of the subsequent works.
Several methods can be used to perform the detection of buried pipes.
The detection via an electromagnetic channel is the most commonly used method. This electromagnetic detection can be performed using electromagnetic detectors based on the active detection of an electromagnetic signal.
A first known method of active detection comprises injecting, using a current generator, an electrical signal in an electrically conductive wire associated with the pipe to be identified and disposed following the line of the latter, and this via connection casings installed at regular intervals along the pipe to serve as access points, and of using an electromagnetic detector arranged to detect an electromagnetic field created by an alternating current flowing in the electrically conductive wire.
Such a detection method proves to be expensive since it requires the installation of a large number of connection casings along the pipe to be detected, each casing being for example disposed either within a technical gallery, or on a non-buried terminal.
Moreover, such a method is not much suitable for the detection of water distribution pipes, since it is difficult to install the connection casings in the vicinity of water systems.
A second known method of active detection comprises injecting, using a current generator, an electrical signal directly in the pipe to be identified when the latter is electrically conductive.
Such a detection method is not suitable for the detection of water pipes, since a large part of the water pipes used are not electrically conductive on the one hand, and the water pipes are mostly inaccessible from the surface on the other hand. Moreover, in the case of cast-iron water pipes, each pipe includes individual elements connected together by elastomeric seals. Thus, an electrical signal injected into the water pipe could not propagate beyond the first elastomer seal, and therefore would make the water pipe monitoring impossible.